Method and apparatus for signal detection, separation and suppression

Abstract

The disclosure relates to methods and devices for separating and suppressing an interfering or jamming signal which is the strongest of a plurality of linearly combined signals and which carries modulation including at least amplitude modulation. The methods and devices collapse the frequency spectrum of the strongest signal to substantially a single frequency and filter out that single frequency.

What is claimed is: 
     
       1. An envelope detector for an input signal of frequency ω comprising: an amplitude limiter for providing an amplitude limited replica of the input signal;   means for multiplying said replica and the input signal; and   means for filtering the product of said multiplying means to pass all frequencies that make up the envelope including DC and block all frequencies that make up a component in said product centered at the frequency 2 ω.   
     
     
       2. An apparatus for generating an output signal having an amplitude proportional to the reciprocal of the amplitude of one of several signals linearly combined in an input signal, comprising: an oscillator for providing a signal having a reference frequency ω o  ;   means for summing the input signal and the reference frequency signal for providing an output sum signal; means for amplitude limiting said output sum signal to produce an amplitude limited sum signal;   a bandpass filter centered about the frequency ω o  for filtering the amplitude limited sum signal; and means for multiplying the input signal with the signal filtered by said bandpass filter.   
     
     
       3. The apparatus of claim 2 further comprising a bandpass filter, centered about the pass band frequency (ω c ) of the apparatus, for filtering the amplitude limited sum signal; thereby providing a signal having the phase of the strongest of the linearly combined signals. 
     
     
       4. A method for generating an output signal having an amplitude proportional to the reciprocal of the amplitude of one of several signals linearly combined in an input signal, comprising the steps of: providing a signal having a reference frequency ω o  ;   summing the input signal and the reference frequency signal to provide an output sum signal;   amplitude limiting the sum signal to provide an amplitude limited replica of the sum signal;   filtering the amplitude limited sum signal to pass frequencies in a band centered about the frequency ω o  ; and   multiplying the input signal with the filtered signal.   
     
     
       5. A method of suppressing an undesired one of two summed cochannel sinusoidal signals, comprising the steps of: amplitude limiting the sum of the two cochannel signals; and   multiplying the frequency of said amplitude-limited sum of signals by a factor k, wherein the value of k is selected responsive to the amplitude ratio, a, of the two cochannel signals such that the Bessel function J o  (ka) is zero.   
     
     
       6. A method of suppressing an undesired one of two summed cochannel sinusoidal signals, comprising the steps of: amplitude clipping the sum of the two cochannel sinusoidal signals which generates a signal whose spectrum comprises (a) a fundamental spectral zone that includes the frequencies of the sum of the two cochannel sinusoidal signals; and   (b) other spectral zones at harmonics of the fundamental zone frequencies; and     filtering said clipped sum to select a spectral zone at a harmonic of the fundamental spectral zone.